Manufacture of articles such as boards and sheets from fibrous vegetable materials



Patented Apr. 27, 1954 mmomerun or Ait'r-Iciatis suoir As compan No Drawing. -np licationssptemher- 1951, Serial No. 245,425

"Claims priorityrtiiplicatiqn great Britain September 1951946 3"Claims.

'I'hiS -appIicatiQn' is a continuation m-part bf --'my-' applieatiom Serf- N0. 1 72,5903, filed Septem- -ber 8, 1947, now ab'andoned.

The presentinvention relates tothe manufacture:of articles suchhas boards and sheets from fibrous I vegetable vmaterials, and *especially from waste' fibrous materials'such as I sawdust, woodshavings, straw; and the-like.

, It ihas already:been riroposed to make bcards -and* sheets from I fibrous vegetable waste :-materia1 by mixing the waste material with a sufficient fquantity of resinous"binders and-shapingthe mixture under heat an'd l pressure *i'nto boards or she'ets. Such boards and sheets, however, 'arei lia-ble to be aiffected by atmospheric conditions unl'ess aihigh proportion of synthetic 1 resin, which is expensi-Vef-thas been inccrporated:therein. 'Moreover, it is-d-iificult to shape-the mixture .mmhomogeneous" boards or "sheets of uniform density afidstrength.

. eIt is a'nother object 'of thein-vention to5provide hard wearing ho'm'og'eneous' b-oards, sheets z"andr. :other articles 0f grainless structure fiand great? mechanical strength, which i are water-reqellent :and moisture resistant.

i-It' is a further object- 'of the invention to en- -able *fibrous vegetable =Waste materials "tobe utilis'ed for"manufacturing boards sheets and other articles, without grading the waste mat'erials in any way or drying them prior to the manutac-z -turin'g process. For-example,-hardwood-sawdust amay'be mixed with-softwood sawdust, and the =mixtu're may "have a -water content of as 'much i as i 40 per cent ormore.

-It =is still "another object of the invention, "in

'the manufacture of boards, sheets and other articles, :to treat fibrous vegetable waste -masterial insucha mannerthat itwill notneces- -=sarily require 'theaddition of any resinor: other bimling agent to impart the desiredmechanical strength *and moisture resistance to the -final product; although, if desired -a small quantity of e 'binding agent :may be-added.

Itkis a particular advantage of "this invention that :sawdust, '=-straw or the :like *material having short fibres may be used without impairing --the desired qualities, such as "strength, homozg'eneity and grainl'es's structure.

-I'n 'ac'eordance with "the present invention,

flip not :1 fibrous =i egetable material impregnated with inorganlc soiids precip'itated within :me pmp.

n'- a more speciflc process of:- this' invention, a

thei nbrous-raw material is prepa'red in which hefibrous material impregnated with ne io morerinorganicsalts m solutionwhich wi11 I cw tne subsequenti pre'cipitation' of insoluble "rganic compounds' within the pulp by-the' sub- -sequent -additionfi'of asuitable th-emiear reagents to the pulp. From the pulp' obtairred after such pr'eci ita'tion hassbe'en efiectedrboards or other 'desire'd farticlesmay be' Tormed imknown *man- .1161,

15 filt' has' been found that the'finely divided *precipitate' of air insoluble inorganic compound or "compounds 'confers, Ven in comparatively small "quantities by weight (for 'e'x'ample- 3' "to *4, per cent f in the flnal' 'erticle) va'luable 1 properties upon' the vfibrous pulp from' 'which the boards :or other 'articl'es are subsequeritly formed.

carrying" out ithe process, the fibrous 'ra'w materialfir'lay first he digested to form a pulp,

-- and th'en thei'pulp impregnated with" a' 'solution 01 ther-choseminorgani'c salt or' s'alts'ior' theprecipit'ation. illterfiatively; thesetwo ste os of the process may he combined: by digesting the ra'w material tvith a' solutibn 'which is also suitable 1 for thei -precipitation.

in a preferred methoii,fibrous-vegetable waste 'n faterial is digested-for about 1 to-4" hours with a weak solution (0 -;5 to- -fisper-cent) ofcaustic :alkalior calciumhydroxide "at a temperature of about 100 -to130 C. The rpulp? so' *obtained is @washed and its water *contnt reduced' to about 50-;per cent. "-I he;15ulp is then intimately mixed "with a -"scmtion of gan inorganic salt or-salts' for impregnating the fibres of *the-digested material. A' wide choiee of inorganic salts is -available for 40 "the impregnation, as-wellas of-rea'gen-ts -forthe precipitation. #For ==example, --s oluble calcium salts,-suchascalcium laypochloriteycalcium' chloride and calcium hydroxide, -'and"=ba1'ium-salts may b'e used:iorimpregnatiommnd insoluble suli phates may bevprecipitated within: the "pulp by adding sulphuric acid or acid salts such as al-uminium 'sulphate. Before-the precipitation' is carried out the fibrous pulp= is suitably diluted and a suflicient quantity of the acidic precipitatbeards, sh'eet's aridetherarticles areimad'e from m agent:- added to recluce the pH-va-lue' of the pulp to between about 3 and 5. If an alkaline salt is used for impregnation and aluminium sulphate used as the precipitating agent, aluminium hydroxide, as well as the insoluble sulphate, is precipitated within the pulp. As another example, insoluble carbonates may be precipitated by the addition of ammonium carbonate or sodium carbonate or by bubbling carbon dioxide through the pulp. If the material is digested with calcium hydroxide, barium hydroxide or any other hydroxide of an alkaline earth, the mixing step may be omitted, and calcium carbonate may be precipitated by the introduction of gaseous carbonic acid or ammonium carbonate into the pulp and particularly hard boards having been obtained from fibrous pulp treated in this manner.

It will be apparent that the quantity of precipitate may be accurately varied whereby a wide range of diiierent types of boards or the like may be obtained.

It is believed that the advantageous results of our invention are due to the fact that the inorganic solids are precipitated within the fibrous structure itself of the material.

After the precipitation has been effected various colouring agents or pigments may be added to the acidified pulp if it is desired to produce coloured boards or other articles. In some cases, a small quantity of a binding agent such as a glue, a water-soluble synthetic resin, rosin-size, an aqueous emulsion of a synthetic resin, or an aqueous emulsion of parailin wax or other waxes may be added. If desired, an inorganic filler may be added to the fibrous organic material before or after digesting it.

Boards, sheets or other articles may be formed in any known manner from the pulp, which may now contain approximately '7 to 10 per cent of solids. For example, the pulp may be poured into a mould of any desired dimension and any desired suitable shape. The mould may be perforated at its bottom so that a large quantity of water is extracted from the pulp through the perforations of the mould, first by gravity and subsequently by the application of a vacuum. A further amount of water may be removed by applying a pressure of up to about 300 lbs. per square inch. Alternatively, the pulp may be further suitably diluted and poured on to a travelling endless wire mesh similar to those used in Fourdrinier machines for the paper manufacture, the pulp forming a wet mat on such wire meshes. Again, a large quantity of water is extracted from the pulp through the wire mesh and a further amount of water is removed by applying pressure. In both cases, a final hot pressing may be applied at a pressure of up to about 500 lbs. per square inch, or the article may be dried by the application of heat without pressure. The density of the article will depend on the pressure applied; if no pressure is applied, the article will have a comparatively low density.

The mould, if used, may have a shape suitable for the production of boards or sheets. It will, however, be appreciated that the mould may have a more complicated shape so as to permit other shaped articles to be produced.

According to a subsidiary feature of the invention, the moisture resistance of the dried boards, sheets, or other articles is considerably improved by subjecting them additionally to heat for about 6 to 24 hours at temperatures of about 100 to 160 C.

In a specific example, sawdust is mixed with 4 ten times its weight of a 1.5 per cent caustic soda solution and treated for three hours at a steam pressure of 40 lbs. per square inch in any suitable pressure vessel. After completion of this digestion the material is washed to remove the excess of caustic soda and is then discharged. It will be found that its water content is about three times the weight of the dry fibres, sufficient water is now removed to reduce the water content to 50 per cent, whereupon the mass is mixed with a previously prepared 5 per cent solution of calcium hypochlorite, the quantity of hypochlorite used being equivalent to per cent of the dry fibres.

After the mixing process has been completed, the resulting pulp is diluted with water to a consistency of 7 per cent. Under continuous stirring, a solution of aluminium sulphate is added in a quantity sufiicient to reduce the pH value to 4.5.

The pulp is now ready to be shaped in accordance with standard practice. Some water may be extracted before the material is subjected to a final drying process in a drying oven or is dried under pressure between heated platens of a hydraulic press. Subsequently, the dry boards, sheets, or other articles so obtained are subjected for hours to a temperature of about 125 C.

Boards and the like produced in the manner described may be treated in a variety of ways in order to make them adaptable to a number of different uses. They may, for instance, be faced with resin, or with resinimpregnated and coloured sheets of paper before or after hot pressing. In this way sheets with highly glossed surfaces are obtained which may be used as tiles.

Owing to the high resistance to wear, the boards may also be used as flooring material.

The boards or the like may be worked in a manner similar to that in which hard wood is worked. As a rule, no fibrous structure is recognisable in the finished article.

It is of course not necessary to remove exactly 50 per cent of the water content from the pulp. In fact, more or somewhat less than 50 per cent of the water content may be removed. I have found, that a removal of 50 per cent of the water content leads to highly satisfactory results and that a removal of this order of magnitude is conveniently achievable in practice with simple mechanical means without rendering the process unduly expensive, although a removal of between to 70 per cent of the water content is admissible.

I claim:

1. The manufacture of articles from fibrous vegetable material, which comprises the steps of mixing the fibrous vegetable material with substantially ten times its weight of a 1.5 per cent caustic soda solution and subjecting the mixture for about three hours to a steam pressure of substantially 40 pounds per square inch to form a pulp, washing the pulp to remove an excess of caustic soda, reducing the water content of the pulp to about per cent, mixing a 5 per cent solution of calcium hypochlorite to the pulp in a quantity of the hypochlorite equivalent to about 10 per cent of the dry fibrous vegetable material, diluting the pulp with water to a consistency of substantially '7 per cent, adding, while the pulp is continuously stirred, a solution of aluminium sulphate to reduce the pH value to 4.5, subsequently forming the articles from the thus treated pulp, and thereafter drying said articles.

2. The manufacture defined in claim 1, where- Ali in as fibrous vegetable material sawdust is employed.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Heaton Mar. 13, 1866 Duemling Nov. 24, 1874 Fletcher Oct. 23, 1877 Just et al. Dec. 14, 1886 Sachsenroder May 22, 1906 Clayton et al. Mar. 9, 1920 Ellis Dec. 16, 1930 Cerini July 21, 1931 Busch Aug. 11, 1931 Bradley Jan. 26, 1932 Campbell et al May 8, 1934 Hartford Oct. 29, 1935 Luth et al. Feb. 11, 1936 Richter Feb. 11, 1936 Dreyfus Sept. 22, 1936 Number Number 15 404 2,251 516,162

Name Date Hempel Mar. 26, 1940 Ellis July 16, 1940 Fleck Nov. 19, 1940 Booth Apr. 6, 1943 Craig Jan. 4, 1949 McEwen Mar. 29, 1949 Brabender et a1. Apr. 5, 1949 Baskin et a1. June 14, 1949 McE-wen July 4, 1950 Craig June 3, 1952 FOREIGN PATENTS Country Date Great Britain of 1869 Great Britain of 1883 Great Britain Dec. 22, 1939 OTHER REFERENCES 20 Ott: Cellulose and Cellulose Derivatives, published by Interscience, New York (1943), page 

1. THE MANUFACTURE OF ARTICLES FROM FIBROUS VEGETABLE MATERIAL, WHICH COMPRISES THE STEPS OF MIXING THE FIBROUS VEGETABLE MATERIAL WITH SUBSTANTIALLY TEN TIMES ITS WEIGHT OF A 1.5 PER CENT CAUSTIC SODA SOLUTION AND SUBJECTING THE MIXTURE FOR ABOUT THREE HOURS TO A STEAM PRESSURE OF SUBSTANTIALLY 40 POUNDS PER SQUARE INCH TO FORM A PULP, WASHING THE PULP TO REMOVE AN EXCESS OF CAUSTIC SODA, REDUCING THE WATER CONTENT OF THE PULP TO ABOUT 50 PER CENT, MIXING A 5 PER CENT SOLUTION OF CALCIUM HYPOCHLORITE TO THE PULP IN A QUANTITY OF THE HYPOCHLORITE EQUIVALENT TO ABOUT 10 PER CENT OF THE DRY FIBROUS VEGETABLE MATERIAL, DILUTING THE PULP WITH WATER TO A CONSISTENCY OF SUBSTANTIALLY 7 PER CENT, ADDING, WHILE THE PULP IS CONTINUOUSLY STIRRED, A SOLUTION OF ALUMINIUM SULPHATE TO REDUCE THE PH VALUE TO 4.5, SUBSEQUENTLY FORMING THE ARTICLES FROM THE THUS TREATED PULP, AND THEREAFTER DRYING SAID ARTICLES. 